Heart Failure (HF) affects ~2% of the western population and ~10% of individuals aged >75 years. Not only is HF already an epidemic, but with the aging of the population, a dramatic further increase in its prevalence is expected. Approximately 50% of patients with HF have a normal ejection fraction (HF with preserved ejection fraction, HFpEF), often called diastolic HF. Many therapeutic interventions are available for HF with reduced ejection fraction, but there is currently no effective intervention available for HFpEF. Given the enormous public health, clinical and societal burden of HFpEF, finding effective therapies for this condition is a top priority in the field. Based on a series of animal experimental and human observational studies that link arterial wave reflections to abnormal left ventricular relaxation, left ventricular remodeling (hypertrophy) and HF risk, we propose a pilot randomized double-blind controlled clinical trial designed to assess whether reducing arterial wave reflections with either isosorbide dinitrate or the combination of isosorbide dinitrate and hydralazine administered for 24 weeks will improve diastolic function, LV remodeling and clinically-relevant endpoints (physical fitness, quality of life) among 42 patients with HFpEF. We therefore aim to: 1) Test whether prolonged nitrate therapy (24 weeks) exerts sustained effects on wave reflections and whether the addition of hydralazine enhances the effect of nitrate therapy on wave reflections in patients with HFpEF. 2) Test whether long-term vasoactive therapy with nitrates + hydralazine results in regression of LV hypertrophy (reduction in LV mass) and LV fibrosis in patients with HFpEF.3) Assess whether nitrate + hydralazine therapy improves diastolic relaxation in patients with HFpEF. 4) Assess whether nitrate + hydralazine therapy results in an improvement in endpoints with immediate clinical relevance (physical fitness and quality of life) in patients with HFpEF. We will also assess whether the effects of vasoactive therapy on LV remodeling, diastolic relaxation, physical fitness and quality of life can be explained by a reduction in arterial wave reflections. If our interventin improves ventricular remodeling, diastolic function and physical fitness, this would introduce a new paradigm in the field and provide a foundation for justifying, designing and powering a more definitive hard endpoint-driven clinical trial in which this approach will be tested as a strategy o improve the outcomes of patients with HFpEF.